1. Field of the Invention
The invention is in the field of radio frequency identification (RFID) devices.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code or other information. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. For example, RFID tags are used in conjunction with security locks in cars, for access control to buildings, and for tracking inventory and parcels.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are RFID devices that are adhesively or otherwise have a surface attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example by use of a plastic fastener, string or other fastening means.
RFID devices include active tags and labels, which include a power source for broadcasting signals, and passive tags and labels, which do not. In the case of passive devices, in order to retrieve the information from the chip, a “base station” or “reader” sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The RFID reader receives and decodes the information from the RFID tag. In general, RFID tags can retain and communicate enough information to uniquely identify individuals, packages, inventory and the like. RFID tags and labels also can be characterized as to those to which information is written only once (although the information may be read repeatedly), and those to which information may be written to repeatedly during use. For example, RFID tags may store environmental data (that may be detected by an associated sensor), logistical histories, state data, etc.
RFID devices further can be characterized as passive, semi-passive, and active RFID devices. Passive RFID devices have no internal power supply. Power for operation of passive RFID devices is provided by the energy in an incoming radio frequency signal received by the device. Most passive RFID devices signal by backscattering the carrier wave from an RF reader. Passive RFID devices have the advantage of simplicity and long life, although performance of them may be limited.
Active RFID devices have their own internal power source, which is used to power an integrated circuit or chip in the device, and broadcast a separate signal. Active RFID devices may be more reliable than passive RFID devices. There may be fewer errors in communication between active tags and readers. Active tags may also transmit at higher power levels than passive RFID devices. However, active RFID devices have the disadvantage of requiring a power source in order to communicate.
Semi-passive RFID devices also have a power source, but unlike active devices this power source is only used to provide that energy for internal operation of the device. In other words, semi-passive devices do not broadcast their own signals, as active RFID devices do. Semi-passive RFID devices usually communicate in a manner similar to that of passive RFID devices, by backscattering an incoming RF carrier signal. Thus semi-passive devices share with active RFID devices the disadvantage of requiring a power source, while ameliorating only some of the disadvantages of passive device communication.
From the foregoing it will be appreciated that improvements in the area of RFID devices would be desirable.